Pen type drug delivery devices have application where regular injection by persons without formal medical training occurs. This may be increasingly common among patients having diabetes where self-treatment enables such patients to conduct effective management of their disease. In practice, such a drug delivery device allows a user to individually select and dispense a number of user variable doses of a medicament. Some aspects of the present invention are not directed to so called fixed dose devices which only allow dispensing of a predefined dose without the possibility to increase or decrease the set dose.
There are basically two types of drug delivery devices: resettable devices (i.e., reusable) and non-resettable (i.e., disposable). For example, disposable pen delivery devices are supplied as self-contained devices. Such self-contained devices do not have removable pre-filled cartridges. Rather, the pre-filled cartridges may not be removed and replaced from these devices without destroying the device itself. Consequently, such disposable devices need not have a resettable dose setting mechanism. Some aspects of the present invention are applicable for both types of devices, i.e. for disposable devices as well as for reusable devices.
A further differentiation of drug delivery device types refers to the drive mechanism: There are devices which are manually driven, e.g. by a user applying a force to an injection button, devices which are driven by a spring or the like and devices which combine these two concepts, i.e. spring assisted devices which still require a user to exert an injection force. The spring-type devices involve springs which are preloaded and springs which are loaded by the user during dose selecting. Some aspects of the present invention are applicable for all of these types of devices, i.e. for devices with or without a drive spring.
These types of pen delivery devices (so named because they often resemble an enlarged fountain pen) are generally comprised of three primary elements: a cartridge section that includes a cartridge often contained within a housing or holder; a needle assembly connected to one end of the cartridge section; and a dosing section connected to the other end of the cartridge section. A cartridge (often referred to as an ampoule) typically includes a reservoir that is filled with a medication (e.g., insulin), a movable rubber type bung or stopper located at one end of the cartridge reservoir, and a top having a pierceable rubber seal located at the other, often necked-down, end. A crimped annular metal band is typically used to hold the rubber seal in place. While the cartridge housing may be typically made of plastic, cartridge reservoirs have historically been made of glass.
The needle assembly is typically a replaceable double-ended needle assembly. Before an injection, a replaceable double-ended needle assembly is attached to one end of the cartridge assembly, a dose is set, and then the set dose is administered. Such removable needle assemblies may be threaded onto, or pushed (i.e., snapped) onto the pierceable seal end of the cartridge assembly.
The dosing section or dose setting mechanism is typically the portion of the pen device that is used to set (select) a dose. During an injection, a spindle or piston rod contained within the dose setting mechanism presses against the bung or stopper of the cartridge. This force causes the medication contained within the cartridge to be injected through an attached needle assembly. After an injection, as generally recommended by most drug delivery device and/or needle assembly manufacturers and suppliers, the needle assembly is removed and discarded.
The dosing section of drug delivery devices for selecting and dispensing a number of user variable doses of a medicament often comprises a display for indicating the selected dose to a user. This is especially important where a user may select a different dose each time depending on the state of health. There are mechanical displays, e.g. a drum with printed numbers on its outer surface, wherein the number corresponding to the actually selected dose is visible through a window or opening in the device. Although such mechanical displays are simple and reliable, they usually require a relatively large construction space which makes the devices bulky. In addition, the size of the numbers is in some cases too small for visually impaired users. Further, electronic displays are known, e.g. LCD displays, which have the benefit of a relatively large number size without requiring too much construction space. However, a downside of electronic displays is that they require an energy source and that such electronic components may be too expensive, especially in a disposable drug delivery device.
It might be desirable designing the housing of the drug delivery device with a non-circular cross-section for example to avoid a bulky appearance of the device, to improve handling due to the non-cylindrical body shape, to reduce the probability of the device rolling from an elevated surface such as a table or shelf and becoming damaged, or to increase differentiation relative to other drug delivery devices. An example of such a non-cylindrical body shape is given in EP 1 414 507 B1, where parts of the housing are oval whereas a dose selector knob is cylindrical.
To prevent the user from accidentally interfering with the dosage selector during the injection and either preventing injection or changing the dialled dose, many injector devices disengage the dosage selector from the drive mechanism during injection. In this case the dosage selector may become locked in place or may rotate freely and not impact on the process of injection. Where the dosage selector is disengaged from the mechanism it is generally regarded as not important as to what orientation the dosage selector is in when it is reengaged to the driving mechanism.
In the case of non-axisymmetric devices or with devices which have a definite home position marked on the dosage selector, it may be desirable that the dosage selector is correctly realigned to the housing when the injection button is released. If the dosage selector is not aligned to the housing, the user may think that the device looks unsightly or may even interpret the misalignment as a mechanical problem. Further, the device might not fit into pockets, bags or carry cases or debris could become trapped between the misaligned faces.